This invention relates to a power generation plant and a power generation method without emission of carbon dioxide and, more particularly, a thermal power generation plant and method of a closed cycle type incorporating a carbon dioxide recovery system.
In a conventional power generation plant, particularly a thermal power generation plant, a steam turbine or gas turbine, or the both are driven by combustion gas energy generated by burning fuel with air in a combustor and the air is also utilized as a working fluid gas compressed in a compressor. In such a thermal power generation plant, natural gas, petroleum fuel gas or coal gas has been utilized for the fuel gas, which generally includes carbon components such as carbon (C), carbon monooxide (CO), or other hydrocarbon (CmHn). Accordingly, the combustion gas after the burning of the fuel in the presence of air includes carbon dioxide (CO.sub.2), nitrogen oxide (NO.sub.x) and sulpher oxide (SO.sub.x) generated by the oxidation of sulfur contained in the fuel in addition to nitrogen gas (N.sub.2) and oxygen gas (O.sub.2) contained in the air.
The exhaust of the harmful gas such as NO.sub.x, SO.sub.x and CO.sub.2, in the atmosphere provides a significant problem for an environmental pollution. It is not easy to restrict the generation of NO.sub.x in the combusion gas as far as the fuel gas is burnt in the presence of air in the combustor and, in order to remove the NO.sub.x and SO.sub.x, in the conventional power plant, additional equipment is incorporated for the removal thereof in the process of gassification and the following gas refining process. In the meantime, in order to remove the CO.sub.2 contained in the gas to be exhausted in the atmosphere after the combustion, it is necessary to remove and recover the CO.sub.2 from the exhaust gas before the emission in the atmosphere.
In order to recover the CO.sub.2 in the exhaust gas, in the conventional practical method, the CO.sub.2 is separated and removed by utilizing a solvent having a property capable of selectively absorbing the CO.sub.2 from the exhaust gas at a low temperature. The solvent including highly concentrated CO.sub.2 also has a property capable of discharging the CO.sub.2 by heating the same, whereby the CO.sub.2 can be recovered by heating the solvent including the highly concentrated CO.sub.2.
However, the method of recovering the CO.sub.2 by utilizing the solvent provides the following problems.
First, the CO.sub.2 is recovered in contact of the exhaust gas to the solvent, but the contacting time is limited; that is, it is impossible to infinitely contact the exhaust gas to the solvent during the operation of the thermal power plant and, accordingly, some amount of the CO.sub.2 remains unrecovered in the exhaust gas. Second, an extremely voluminous CO.sub.2 is usually generated in the thermal power plant, so that the voluminous solvent is also required as well as the heat energy for heating the solvent, which results in the increasing of the cost for the construction of a CO.sub.2 recovery system and of the operation cost thereof.
In the other point of view, in the conventional thermal power plant, the air including about 80% of N.sub.z is utilized for burning the fuel and the exhaust gas includes a voluminous highly concentrated N.sub.2 gas, so that the total amount of the exhaust gas increases and a large amount of the solvent for recovering the CO.sub.2 is required as described above.